Two-motion cam controlled automatic telephone switch



DOC. 23, 1947. B K 2,433,256

TWO-MOTION CAM CONTROLLED AUTOMATIC TELEPHONE SWITCH Filed March a, 1943 '7 Sheets-Sheet 1 INVE NTOR GEORGE THOMAS BAKER ATTORNEY Dec. 23, 1947. e. T. BAKER 2,433,255

TWO-MOTION CAM CONTROLLED AUTOMATIC TELEPHONE SWITCH Filed March 6, 1943 7 Sheets-Sheet 2 INVENTOR ozone: moms BAKER av zg. 4

ATTORNEY Dec, 23, 1947. cs. T. BAKER 2,433,256

TWQMOTION CAM CQNTROLLED AUTOMATIC TELEPHONE SWITCH Filed March 6, 1943 7 Sheets-Sheet 3 .F'i 4. 31 31a 15 71 INVENTOR GEORGE THOMAS BAKER ATTOR N EY Dec. 23, 1947. G. T. BAKER 2,433,256

TWO-MOTION CAM CONTROLLED AUTOMATIC TELEPHONE SWITCH Filed March a, 194:5 7 Sheets-Sheet 4 INVENTOR GEORGE THOMAS BAKER ATTORNEY Dec. 23, 1947. BAKER 2,433,256

'EWO-MOTION CAM CONTROLLED AUTOMATIC TELEPHONE SWITCH Filed March 6, 1943 T Sheets-Sheet 5 I N V E N TOR GEORGE THOMAS BAKER ATTORNEY Dec. 23, 1947. BAKER 2,433,256

TWO-MOTION CAM CONTROLLED AUTOMATIC TELEPHONE SWITCH Filed March 6, 1943 7 Sheets-Sheet 6 Q mvsu TOR eeoae: moms BAKER zzaag,

ATTORNEY Dec. 23, 1947. G. T. BAKER 2,433,256

TWO-MOTION CAM CONTROLLED AUTOMATIC TELEPHONE SWITCH Filed March 6, 1943 7 Sheets-Sheet '7 mvzufon ezonee moms BAKER ATTORNEY Patented Dec. 23, 1947 TWO-MOTION CAM CONTROLLED AUTO- MATIC TELEPHONE SWITCH George Thomas Baker, Liverpool, England, as-

signor, by mesne assignments, to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application March 6, 1943. Serial No. 478,242 In Great Britain April 20, 1942 39 Claims.

The present invention concerns improvements in Or relating to the construction of selector switches as used in automatic telephony, and the object of the invention is to provide a construction of selector switches which combines efiiciency in operation, smoothness of running and compactness in design, so as to meet the fundamental requirements of an automatic telephone system in a very satisfactory manner.

According to one feature of the invention the contact-making arms of a selector are caused to move in two directions in substantially the same plane by a common rotating member having its axis substantially normal to said plane separate clutch mechanisms being provided to enable the rotating member to move the contact-making arms successively in the two directions.

According to a further feature of the invention the contact-making arms of a selector which are adapted to be moved across and into a bank of contacts are subsequentl moved in a direction substantially normal to the plane of the first movement to cause pairs of contacts of a selected set of contacts to engage.

According to a further feature of the invention the step-by-step movement of the selector mechanism is effected by a roller having two cam surfaces one of which acts on a driving roller and the other of which acts on a fixed surface, whereby the first roller is given a movement in a close path to cause a tooth-engaging action to take place followed in succession by a tooth-driving. a tooth-disengaging and a restoring action to advance the selector mechanism one step.

According to a. further feature of the invention an arm having a tooth-engaging member at one end and a double cam arrangement pivoted at the other is so arranged that the pivot of the den. ble cam arrangement is given a movement due to the action of the two cams jointly on a fixed and moving surface respectively to cause the toothengaging member to move in a substantially rectangular path to enter, drive, and leave a tooth of the selector mechanism and return to its starting position, whereby the selector mechanism is advanced one step.

According to a further feature of the invention a selector switch mechanism, that is to say the operative part of the selector switch as distinct from the contact banks is adapted to be jacked into a contact bank having fixed and movable contacts comprising a horizontal frame carrying on one side an electromagnet and on another side at right angles to the first side a second electromagnet, the said electromagnets controlling the motion of contact-making arms in difierent directions from a common rotating shaft.

(Cl. 17927.5Z)

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings, which correspond to similar figures in my copending application No. 478, 45, filed March 6, 1943, now Patent No. 2,- 402,232, dated June 18, 1946, in which is disclosed a full description of the selector mechanisms and circuits, selector bank construction and cabling and mounting arrangements for a new and improved automatic telephone system with which the present invention has direct association.

Referring now to the drawings,

Fig. 1 shows an enlarged perspective part view of a rectilinear continuous bank showing the metal strip multiples and the precious metal contacts, a desired connection being efiected by the appropriate operation of cordless contact-operating arms, conveniently referred to hereinafter as wiper arms.

Figs. 2 and 3 together show the circuit of a tenlevel ten-outlet per level group selector and the basic control circuit therefor.

Fig. 4 shows a reduced diagrammatic plan view of a cam driven two-stage selector and also the position occupied by the bank with respect thereto. Fig. 4a shows a plan view of the primary carriage release control mechanism with the carriage in its normal position, while Fig. 4b is a similar view of the conditions obtaining when the switch has completed the secondary release movement from the position to which it has been previously set and is about to commence its primary release movement.

Fig. 5 shows a part diagrammatic side elevational view of the two-stage selector and its associated bank and approximates its full size.

Fig. 6 shows a reduced perspective view of the selector chassis with the selector components assembled thereon.

Fig. 7 shows the slight mechanical modifications which are involved in meeting special release action requirements.

Fig. 8 shows an enlarged end view of one end of one leg of a carriage shown on its running rail, while Fig. 9 shows an enlarged perspective view of the primary and secondary carriages together with the wiper arms.

Fig. 10 shows an enlarged sectional view of the primary drive main and subsidiary cams, which, as shown, are integral with one another, while Fig. 11 shows an enlarged perspective view of the selector secondary drive arrangements from which, for the sake of clarity, the main drive cam is assumed to have been removed. The four basic stages of operation involved in driving the selector primary carriage one step are shown in the four Figs. 12 to 12c inclusive.

Fig. '13 shows reduced erspective view oi the complete selector jacked in position adjacent the bank.

The two basic movements performed by the welecting switch wiper arms with respect to the contact bank are across" and in, and wfil be referred to as primary and secondary movements respectively, and bein eifected by primary and secondary main and subsidiaryd'rlvlng cams.

With regard to Fig. 4 it should be explained that it is partly diagrammatic and not in exact accordance with the exact commotion. For mstance, the drivin cams are shown mom!- with 1 5 a central pivot and overlapping the continuously operating roller, whereas the primary cam should be of the shape shown in Fig. 12 and should be pivoted eccentrically as shown. The secondary "driving cam which is adapted to advance the secondary'carriage through two steps per revolution is or the same size as the primary cam, but "the shaped both this secondary cam and its subsid- Terry cam is inodined'according'ly. theshapeoi the subsidiary'ca'm being on the lines indicated inthe perspective view of Fig. '11. 7

A further point by which the selector shown in Fig. 4 differs from actual practice is that the primary cam is shown to be of the two-stage escapement release type while the secondary cam is shown to be or the -single-stage-sirnple release type so that "the former is only released and a1- lowe'd to engage with the driving roller when the correspondmg controlling relay releases alter having been operated, "while the latter is released and allowed to engage with the roller as "soon as the secondary control relay operates. With the simple circuit arrangements to be described the selectoris therefore only suitable for functioning in a group selecting capacity when "it has to respond to trains 01' impulses for its primary direction of movement and when it has to selfdrive in the secondary direction so as to perform a hunting operation. 'Both primary and secondary cams may be of the simple catch release type shown in connection with the secondary cam in Fig. 4 if the circuit arrangements are suitably modified.

Referring to Fig. 4 it will be seen that the .power source for the operation of the selector is derived from a'hard rubber roller 41., rotating on a common shaft at a constant speed, say 10 R. P. 'S. The primary and secondary (driving cams l8 and 49 are each eccentric and pivoted so as .tobe Just clear of the roller on its smallest radius. Each camhas a spring 12 or 64 associated with it which stores sufflcient energy to give the cam a small rotational movement when a catch controlledby a control relay Tll or 15 is released. When a control relay has effectively released the catch the 'suriace of the cam after a. slight movement comes into contact with the roller which continues the rotation of the cam. As is later fully described, the pivotal 'the cam is moved away 'from the roller as the cam "rotates, the pressure between the cam and the roller due to the load automatically preventing slipping. The pivot of the cam transmits its movement 'by a single 'meniber W6 or 61) direct to a carriage '50 or 52. A subsidiary cam integral with the main cam and "operatingupon a 'hxed "surface causes the driving pin 81 to be moved in and out of engagementwith the drivingteeth thus avoiding ratchet and pawls andensuring a constant lock of the carriage at all times. The contour of the main cam is such as to give constant acceleration and deceleration to the carriagc thus reducing stresses to a minimum.

The switch is built up upon a chassis 3| on which the primary and secondary control relays I4, 15 are mounted, either directly or indirectly as will be later described. Two carriages are provided, a U-shaped primary carriage 52 (see Fig. 9'), the two side arms 53 and 54 of which form the wiper arms, and an L-shaped secondary 50, on the long arm 5| of which the primary carriage is adapted to run. Each of the carriages runs on rollers and is provided with a liooiil rcd driving member, the primary carriage being adapted to be moved step-by-step on a rail provided "by the long arm of the secondary carriage and thus to carry with it the wiper arms 53 middle. state of balance therefor being maintained by the wiper arms which rest on a rail '3! positioned at right angles thereto and forming an extension of the release magnet armatime 52 (see also Fig. 6). The secondary "carriage is adapted to be moved step-by-step on rails provided by the chassis and thus to carry with'itthe primary carriage and associated wiper arms.

As an introduction to the operation of the switch it will be assumed that it is functioning 'as a final selector, i. e., both basic movements are controlled by dialled impulses.

In this case both primary and secondary cams will have to be of the two-stage release type or alternatively suitable circuit arrangements will have to be provided to allow of impulse control of single-stage release cams.

On receipt of the first train of impulses, the primary relay "I4 responds and in a manner to be "later described intermittently couples the associated driving cam 48 with the roller drive 41 with the result that a driving member 76 pivoted on .thesame pivot as the cam is given a reciproeating androcking motion and its tip co-operates with the toothed driving member of the primary carriage 52 to advance it a number of steps corresponding to the number of impulses dialled and thereupon .to set the wiper arms to a position opposite the required bank level. The release magnet 18 is then energised, whereupon rail 34 secured to the magnet armature 32 raises the wiper arms '53 and 54 slightly at their tips so as to cause these tips to clear the toothed combs 24 of the bank level into which they will be subsequently inserted. The banks consist of fixed contact members 23 extending from one side of the switch to the opposite side in the form of metallic .strips and movable contact members, 'ohoforcach fixed contact member in each switch which formthe teeth of a comb 24, insulators I2 being provided between the comb plates and strips as illustrated in Fig. '1. The second train ofrreceived impulses is effective on the secondary relay 15 which in response thereto intermittently *oouples 'the associated driving cam 49 with the roller drive and the secondary driving member "B1! is also given a reciprocating and rocking moition so :as to cause the secondary carriage 50 to move a number of steps corresponding to the digit concerned and in so doing to carry with it the primary carriage and also the wiper arms mounted thereon. At the end of the second digit the wiper arm. tips will be positioned over the required set of contacts in the bank and the relcasemagnet is now de-energized to cause the tips to lower into the contact sets opposite to which they are positioned in order to make firm contact between the incoming trunk and the selected outgoing trunk.

When the switch is to be released the release magnet is again energised and it will be understood that the mechanical conditions of the primary and secondary ratchet retaining pawls are made such as to allow the carriages to restore to their normal positions under local spring tension, the wipers travelling light as during the initial setting operation of the switch, since the wipers will have again been lifted clear of the banks on the energisation of the release magnet.

Consideration will first be given to the general assembly and construction of a selector switch bank and for this purpose reference should be had to Fig. l.

A bank is formed by continuous strips 23 running the full length of the predetermined multiple and as shown in the part view of Fig. 1 these are clamped at opposite sides of selectors to form fixed contact members, the intervening space between the clampings forming the bank contacts for one selector. At the end of the multiple the strips 23 are fanned out to form wiring tags. That part of the bank multiple allocated per selector will subsequently be referred to as a selector bank 50 that Fig. 1 may be described as showing a part view of two selector banks in each of which are included three levels of two conductors each. A level of one bank is moreover assumed to have been broken away in order more closely to illustrate its construction. Each bank will be preferably of the 100 point type, that is to say, with ten rows or levels of ten sets of contacts, each set of contacts being formed on four strips and four combs 24; On each level there will be provided in addition the usual eleventh step set of contacts for overflow busy indication purposes.

A multiple will usually comprise twenty such banks assembled together one above the other, the necessary multipling being inherently performed by virtue of the use of continuous strips 23 which connect with the outgoing trunks. The connecting function of the ordinary selector wipers and cords is taken by a set of comb plates 24 one of which is provided for each row of strips conveniently referred to as a level of each bank and having fingers 26 aligned with the various bank strips. Each finger of a comb plate such a 24 forms a movable contact member. All bank contacts are made of precious metal such as silver, and to make this a commercial proposition all the silver-base metal junctions are made by rolling, this rolling operation being carried out in the stock before blanking.

The continuous strips are stamped from a metal sheet on which silver contact trips will have been previously rolled at right angles to the direction of the strips and at spacings of say 1 inches. this distance representing the calculated vertical distance required between bank centres to accommodate the selector switches one above another. The comb plates are stamped from springy metal ribbon of suitable width and provided with a rolled silver edge of, say, about mils width. The comb plate fingers are preferably each split with a saw out (not shown) to give a twin contact effeet and the plates are subsequently formed to give the requisite shape shown in Fig. 1.

Each row of contact members in a bank is separated from its neighbour by an insulating plate [2 of a length equal to that of the comb plates and of a thickness or say 50 mils to reduce possible cross talk to a minimum and at the same time to give ample room in the level for the insertion of the Wiper arms. Since each strip will be clamped in each of the twenty banks through which they pass, it is not considered necessary to rovide clamping bars which extend through the banks, and accordingly it will be seen from Figs. 4 and 13 and particularly from my cc-pending application No. 478,241, filed March 6, 1943, that each bank of the multiple after assembly in a suitable jig will be clamped together by two horizontal clamp plates such as I3 and M which are secured against the bank by clamp rods such as l5 and I6. The requisite spacing of 1%.; inches between adjacent banks is secured by means of the four vertical members I1, l8, l9 and 20 which extend over the length of the multiple and which are secured at each bank by the two clamp rods provided individual thereto.

As will be described later each selector switch mechanism is adapted to jack into position against its bank in the manner shown in Fig. 13, with its wiper arms normally at rest at a distance equal to one level before the first level of the bank. To meet this requirement suitable packing pieces 2| and 22 (Fig. 4) are interposed between vertical bars l9 and 20 and the adjacent clamp bar It. From Fig. 4 it will be seen that the clamp rod IE will be nearest to the selector switch mechanism and this will be of such a length as to'finish off level with the vertical members I 'l and 19 including its fixing nuts, or alternatively countersunk fixing screws may be used as in Fig. 13. The other clamp rod IE will be of such a length as to extend for about of an inch at one end in order to provide suitable support for the bank multiple on the mounting upright.

In the development of the new automatic telephone system in which the selector according to the present invention forms a large part, mechanical and electrical design were both taken into consideration, and at this stage a preliminary circuit review will be introduced since some of the circuit aspects of the system had a very large influence on the final design.

It will, however, be appreciated that certain of the mechanical features are capable of being used independently of the circuit design and Vice versa, the present invention aiming at showing how the two features of design may be combined with advantage.

It has been noted that one of the major differences between this selector switch and its prototypes is that the connecting function is now part of the bank and virtually divorced from the selector. It seems highly desirable to maintain this condition rigidly not only for selector simplification but also for talking efficiency, Hence all switching contacts must be kept out of the through wires and every selector must look like the right-hand portion of Fig. 3, from which it will be seen that the speaking path at each selector passes through neither relay contacts nor jack-in plug and socket joints.

In designing circuits to meet this condition the following guiding factors were taken into consideration:

1. It is extremely advisable that the holding and battery feeding bridge shall be in the first stage or at least in an early position in the train.

2. The avoidance of line contacts means that selectors provided with two or more sets of wiper arms and banks should not be provided as these need switching relays so that generally there will be only one available outlet per step on any level such as on a 100 outlet (ten levels of ten outlets each) selector and it is proposed to use such a 100 outlet selector in the new system. The new selector drive arrangements may, however, enable a secondary movement search speed to be obtained, which will permit of fifteen or more outlets to be hunted over in a direct line. The use of such selectors also permits four wires to be used and this fourth wire is made use of to simplify subsequent circuit design. It also simplifies the circuit problems which arise when a. feeding bridge is employed at any early stage in the switch train.

3. The use of the fourth wire opens up the possibility of avoiding the use of independent relays in the selectors. The primary and secondary magnets may be used as relays, since they can conveniently be of the same general design as the standard British post oflice type relays.

4. The necessity of eliminating an extra mounting means for relays enables the selector to assume whatever shape is most suitable for its own purpose and it is found that a fiat type of construction with a height only of the order of 1 /2 inches is quite possible.

Every selector normally contains three basic relays usually designated A, B and C. The present circuits are such that these relays need be provided only once per train thus further justitying the use of 100 outlet selectors and efiecting material economies in relays.

One of the problems reated by employing the battery feeding relays at an early stage in the connection is that of impulsing. In this case the relays usually subject to impulse failure are concentrated in the first stage so no difference is encountered there. The magnets are subject to an initial extra repetition due to this cause, but in any case, this is met by the elimination of a repetition in the selectors themselves where the incoming impulses are delivered direct into the magnets instead of being repeated from an A relay. In addition to this, the magnets are self-correcting and will perform a single operation on one pulse however long or short.

Figs. 2 and 3 show the fundamentals of the new circuits. The combined primary magnet and relay VB. is impulsed directly over the negative line, only one step being taken for each up and down movement of the relay.

The Z wire is used for primary/secondary changeover by the operation of the combined release magnet and relay ZR. This unit is of comparatively high resistance and hence little battery drain is involved in maintaining it energised until the completion of the secondary movement. Immediately this motion commences rclay VR, which also serves as the switch holding relay, is maintained from the private and on its release at the end of the call re-energises the release magnet to initiate release of the switch.

The only controls to reach the selector come over the four incoming wires. All tones and common services are supplied at the battery feeding relays. Accordingly it would appear that only battery and earth connections are required in addition to the four control wires. Hence a six point test jack has been used in place of the usual U-point jack. Where selectors have to fulfill some special function this number would undoubtedly be increased but if the selector is definitely kept solely to its mechanical functions the number required is quite small.

A detailed description of these circuits will be made later after consideration has been given to the selector switch mechanism, for which reference should be had firstly to the plan layout thereof shown in Fig. 4. From this figure it will be noted that it has been possible to accommodate a two-coil release magnet 78 so that ample power is available to meet the requirements of both the switch release and wiper arm control functions which it is adapted to perform.

In Fig. 6 is shown a view of the pressed steel selector chassis 3! with the components assembled thereon. The manufacturing operations of the chassis consist of blanking and part forming, followed by a final forming operation, the latter being limited to the completion of the side lips. Upstanding portions in the centre of the chassis may be formed integral with the chassis 3| for the purpose of supporting certain spring sets, coils, and also the release magnet armature pivots or a U shaped sub-assembly could be provided having the advantages that:

(1) The springs can be assembled on the subassembly before mounting on the chassis and the use of an offset screw driver is avoided.

(2) An adjustment in the vertical plane can be provided if desired.

The end slot on the plug-ended arm 31a. of the chassis is not required if this arm is located between the separators supporting the jack on the bank vertical member and both bank clamp rods are countersunk on this side of the bank.

As regards the assembly of components on the chassis the release magnet armature 32 will first be fitted and its pivot pins will be riveted in position; the two extension arms of this armature will have been previously linked by the wiper rails 46 and 34, one of which. 34, is connected to one end of a coil spring 35 which serves as the armature return spring. The release magnet and secondary off-normal spring sets 40 and 4| respectively may then be fitted, the usual buffer blocks for which will be secured to the base of the chassis. The secondary carriage retaining pawl 33, together with its return spring (not shown), is riveted into place in such a manner that its rivet 41 serves as a pivot on which it can turn. This pawl is provided with a springloaded pivoted piece 39 at its head which pivots on the rotary ratchet pawl pin I22 and is used in conjunction with the rotary release as will be described later. Also attached at this stage to arm 31:: of the chassis is the six point plug 31 which is adapted to engage with a jack secured to one of the bank vertical members when the switch is jacked into position.

Before referring to Fig. 9 which shows the primary and secondary carriages, it is desirable to point out that it was originally intended to grind and harden the lip shown on the right hand side 3!?) of the chassis in Fig. 6 but differential hardening especially of a piece this size is rather a diificult manufacturing operation and to avoid this a separate running rail of hard steel is .employed say of an inch thick by an inch wide, as shown in Fig. 8 where it is designated I3l, with a top contour to suit the trolleys as described later, the corresponding upright 3Ib of the chassis side being finished straight and the rail is screwed to the inside. This change assists the manufacture of the chassis since the only sharp turn has been abolished. This permits of the use of a harder quality steel with consequently greater rigidity. The other lip which contacts a flat roller required no such modification.

Referring to Fig. 9 it will be seen that the L- shaped secondary carriage comprises a short arm 50 and a long arm 51, the latter forming the running rail for the primary carriage 52 and its wiper arms 53 and 54. The rail 51 1W5 1 5!? to match the rollers, which ridge may be pressed up. Preferably if as is anticipated suillcient length of both this and the secondary running rail should be required then a special roller stock which would be cut oil to the desired length would be used.

The wiper arms 53 and 54 are pressed from stiff steel of the order of mils thick so as to form channel-shaped members. These arms are riveted to the member 52 and rigidity is provided by the bracing piece 19, riveted to the centre of the carriage and to the wiper arms at the point reached by the bank when the wiper is on the llth bank contact.

Each contact operating tip is moulded on. One of the plastic resins, e. g., Bakelite, may be used for this purpose. or failing this, it may consist of two ebonite or like pieces riveted on. In either case the lower side of the wiper arm is flattened at the actual wiper tip to provide a central sup- D0113.

Ordinary rubbing wipers (not shown) when re: quired for instance for testin for a free outlet, lie along the fiat part of the wiper arm on either side. They are made of any of the usual Wiper materials, e. g., phosphor bronze, and are riveted to the wiper arm behind the tip. Such rivets include insulators, the inner pair of which are carried along the arm to prevent contact with the arm. The rear tags are carried to a second rivet about two inches behind the tip at which point the wiper cords are attached, thus obviating the need for the cords entering the bank.

The carriage return springs 80 and BI lie along.- side their respective carriages in each case on the outside thereof as shown in Fig. 4.

To keep the trolleys on the rails it is proposed to magnetise the latter. These are already of a hard steel and the trolleys and carriage provide an efficient return circuit. There should be no difficulty in obtaining the required retaining force.

There are components of the switch mechanism which have not yet been dealt with, or at least have only been mentioned generally, and the design and functions of the members involved will be better appreciated from the ensuing paragraphs which proceed step-by-step with the mechanical operations involved in the setting up and subsequent release of a group selector switch, i. e., with dialled primary movement and self? driven secondary movement.

Referring now to Fig. 4 the primary and secondary control relays I4 and T5 are of the British post ofiice standard type with extensions 82 and 83 on their respective armatures for cam control purposes. As previously mentioned, on the secondary movement these controls take the form of a simple catch that is released when the relay is energised, but for the primary movement escapement control is provided necessitating one up and one down movement to cause release. 0n the primary driving cam 48 the co-operating part of the escapement catch comprises the two upstandins pins H0 and HI, while on the secondary driving cam 49 the co-operating part of the simple catch is either pin H2 or pin H3 which are spaced in 180 degrees phase relationship so as to allow of a half rotation only of the cam for each release of the catch, it being appreciated that the cam is designed so as to advance the $99151 ca riage. two step 0 every revoluthan. previously mentioned the control relays are supported by brackets which form the top plates of the two spring build-ups on each relay. Two b a k ts a e t us used p rel y. o e P bui d up. nd on t pr mary relay the snee e H4 s su t d by a c annel me b r H5 F 5) e e ng acro s t e cha sis u e the arr a e ail 51 and the ower one, H5 is secu d to the floor oi the chass 3 itself. The seconda y lay brack ts on f wh h i s wn esigna ed H1 in Fig. 4, are secu d to a U-s c- 19 ang e p ece 89 shown in Fig. l but not in F and he ba o wh ch i bo te to e sid f t hass the s d arms r th angle ni e each su portin a acket- The pr b em o prima y nd ec nda y driV of the switch is essentially a dynamic one in contrast to the stationary elements which have already been discussed. Lightness of the moving parts is absolutely essential and with the con.- structlon about to be described the weight of the moving unit has been brought down to just over half an ounce.

The main improvement is that while in the construction according to the prior application two moving parts were employed one having a purely reciprocating motion, the other partaking in the reciprocating motion and having in addition a further rocking movement which causes the pawl tip to move in and out of the teeth, the construction according to the invention employs only a single piece 60 or 16 (Fig. 4) which has both reciprocating and rocking motion superimposed.

Referring to Fig. 11, the simplest drive would consist of a single strip joining the pivot of the main cam and the driving pin, but in the construction which is herein illustrated such a strip would foul the control relay armature retaining screw and the strip is bent accordingly to miss this screw. The movement is effected by the joint action of two cams, the driving cam which engages with the surface of the continuously rotating driving shaft or its equivalent and a subsidiary cam which engages with a stationary surface and while th driving cam is being rotated serves to deflect the end of the strip in a directime more or less normal to the direction of reel! mention.

The main component is the driving cam, which does the actual stepping of the selector. It is assumed that the cam moves in a straight line but in fact at each end of the stroke it is caused to move at right angles to the direction of travel under the influence of the subsidiary cam. This movement occurs when the cam contour is sub, stantlelly fiat and has the effect of starting to more the pin in and out of engagement while still travelling. If this is found to have any detrimental effect in practice a few degrees of fiat will be allowed at the appropriate points.

The data used to design this cam was obtained as hollows: The primary and secondary relays have been located as shown in Fig. 8 and if lines representing an imaginary cover I32 are drawn outside these relays, then the roller drive should tit inside this space. The continuation of the ch s s l e mu t be such that the roller must not interfere with the withdrawal of the chassis. Also the centre of the roller must be symmetrically aligned with regard to the two drives. These my; fix the roller diameter at say two inches.

If a line is drawn joining the roller centre and h d ing n h in t en tooth, t centre of the driving cam preferably lies on this line. It follows that the mean effective diameter of the cam is something over an inch, say, 1.2 inches.

The minimum period available between two successive digits is normally taken as 450 milliseconds, this being fixed by the dial switch. Of this, 150 milli-seconds is allowed for the release of the C of digit-train relay, leaving 300 milliseconds to perform the automatic hunting operation. Hence 30 milli-seconds is available per step giving a hunting speed of 33.3 steps per second.

The primary stepping speed must be such as to be higher than that of the fastest dial likely to be encountered. In practice dials are assumed not to exceed 14 impulses per second, and allowing a margin the vertical speed should be about 16 per second.

It will be noted that this is about half the secondary speed, and since both cams function from the same roller and are required to be about the same over-all size, it follows that the secondary cam must perform two operations per revolution and the primary, one. That is to say, th secondary cam is provided with two pins diametrically opposite and the shape of the driving cam and subsidiary cam is modified accordingly. The subsidiary cam shown in Fig. 15 is designed for the secondary movement to work with two steps per revolution. Alternatively the cams may be adjusted in size.

The revolutions per second ratio between the primary cam and roller is about 0.6 giving the latter a speed of 9.5 revs. per second. Now in automatic telephony 10 impulses per second being the basic dialling speed is most widely used. Now if the shaft speed is made 10 revs. per second it can be used to provide any machine-made impulses required and many other advantages will be obvious. Hence the roller will preferably be two inches diameter with a speed of 10 revs. per second.

The primary speed will be made exactly half the secondary, giving a stepping time of 60 milliseconds. The usual division of an impulse in telephony is 66% for the operate stroke and the remainder for the release, and this ratio will be retained. Hence the forward primary stroke occupies 40 milliseconds and the return, 20 milliseconds. The secondary of course uses half these times.

In response to a train of dialled impulses the primary relay 14 responds and advances primary carriage 52 along the long arm of the secondary carriage a number of steps corresponding to the digit dialled and thereupon sets the wiper arms carried by carriage 52 to a position opposite the required bank level. This is performed in the following manner.

From reference to Fig. 12 of the four operational views of the primary drive arrangement, Figs. l2-l2c, it will be seen that the main primary driving cam 48 has integral therewith a subsidiary cam 13 constructed for instance in the manner shown in Fig. 10. The latter is urged by spring 12 against the case hardened runner 11 which forms part of the bracket 84 on which is mounted the case hardened pivoting roller 85 and which is conveniently secured to channel member H5 extending across the chassis as shown in Fig. 5. The roller 85 provides the main pivot of the driving strip and gives both a rol-ing and rocking point for the travel and rock of the driving member 16. The driving strip 16 is pivoted at one end on the same pivot 86 as in the main and subsidiary primary cams and at the other end carries a driving pin 81, it being understood that the pivot 86 is independent of the bracket 84 so that the driving strip and cam assembly is maintained in position solely by being urged by spring 12 against runner 11 and roller 85, spring 12 having a component of its pull lying between these supports so as to give pressur on each. In order to advance the primary carriage through one step the driving pin 81 is adapted to be given a substantially rectangular movement. The first stage is due mainly to the subsidiary cam being pressed against the slide plate 11 to cause the driving strip 16 to pivot about 85 and the pin 81 to engage with a tooth of the toothed driving member 66 as shown in Fig. 12a, the second stage which is due mainly to the main cam 48 due to its engagement with the roller 41 moving the pivot 86 away from the roller and so causing the pin 81 to advance the carriage driving strip 66 along the running rail 5| to the position shown in Fig. 12b, the third stage is the withdrawing of the pin from a ratchet after a complete step has been made to the position shown in Fig. 120, due to the subsidiary cam and the runner and the fourth stage is the restoration of the pin back to the position shown in Fig. 12 due to the main cam and the roller.

In the normal position, i. e., with the main cam 48 held by the catch 82/ll0 the subsidiary cam 13 is on its maximum radius as shown in Fig. 12.

When the control relay 14 is operated on seizure of the selector. the catch 82 will move to the left away from the stop I I0, the amount of movement being such however that it will still remain in the path of the following stop I. Cam 13 thereupon rolls on slide plate 11 under pressure of spring 12 and cam 48 rotates with it for a short movement, further rotation being prevented by the engagement of stop i II with catch 82. This slight rotational movement brings the periphery of cam 48 a little nearer the roller 41 owing to its radius gradually increasing, but contact does not yet take place.

When the control relay releases in response to the first break impulse of an impulse train the catch 82 will restore to the position shown. In the engaging face of catch 82 a U-shaped recess is cut in such a position and of such size that the stop III will just pass through, and cam 48 will now continue to rotate forward under pressure of spring 12 until the increased angular movement brings it into contact with the driving roller 41 with which it will remain in frictional engagement for the remainder of the revolution.

The first effective stage in the rotational movement is reached when the subsidiary cam has moved from having its maximum radius in contact with slide plate 11 to where it comes to have its minimum radius in contact as shown in Fig. 16a. During this stage the pivot 86 will have moved to the left to cause the driving pin 81 to engage with the top tooth of the primary carriage 52.

From this point onward the radius of cam 48 in contact with roller 41 continues to increase, while the radius of the subsidiary cam 13 in contact with slide plate 11 remains constant so that the driving pin 81 is given a movement in a direction along the path of the teeth of carriage 52 which is advanced one step when the position shown in Fig. 121) is reached. This completes the second effective stage.

For the third efiective stage the radius of cam 13 48 in contact with the roller 41 then remains substantially constant, while that of cam I3 in contact with slide plate 11 rapidly increases so that the driving pin is withdrawn to the position shown in Fig. 120.

The fourth and final stage consists of the driving pin being moved back to the position shown in Fig. 12 and is effected as the continued rotation of the cam 48 with its radius in contact with roller 4'! decreasing proceeds. At this stage the toothed plate 66 is one step higher up than shown in Fig. 12.

On the next operation of the control relay and its subsequent release a second cycle of operations as described is performed to advance the carriage a further step and so on until the carriage together with the wiper arms which it carries have been set to a position opposite the required bank level.

Referring again to Figs. 4 and 12 it will be seen that lying along the primary carriage is a retaining pawl 43 which is attached by a pivot to the secondary carriage 50 and carries a case hardened retaining pin H8 at its free extremity which engages a tooth in the opposite side of the primary carriage to the driving teeth. At the free extremity of retaining pawl 43 there is provided a projection H9 at right angles thereto which passes under the carriage so that its tip will co-operate with an edge of the primary driving pawl 16. The receipt of an impulse causes the primary driving pin 81 to perform a rectangular movement as described and as the pin moves inward into engagement with the primary carriage ratchet the projection on the retaining pawl in engaging with the driving arm pushes the retaining pin IIB out of its tooth as shown in Fig. 12a. When the driving pin has completed its forward travel and carried with it the primary carriage through one step the retaining pawl and its projection assume the position shown in Fig. 121), while when the driving pin withdraws at the end of its travel as in Fig. 120 the retaining pin H8 drops back in to the next tooth, the distances between teeth being such as to permit this to take place so that one is always in engagement. These operations take place for each impulse of the impulse train, and it will be seen that a positive lock is at all times maintained on the primary carriage by the driving pin or :by the retaining pin so that overshooting cannot take place.

From reference to Fig. 4 it will be seen that a projection i211 is carried on the primary carriage 52 and this in the normal position of the carriage presses on the upper spring set I21 asso-- ciated with primary relay l4. Springs |2i constitute the oil-normal springs which change their position when pressure is removed, to produce suitable circuit operations as soon as the primary carriage 52 commences its first step. They are, of course, not affected by operation of the primary relay armature which is eflective only on the lower spring set associated with the relay.

At the end of the impulse train the circuit arrangements are such that the release magnet 18 is energised, whereupon the rail 34 secured to armature 32 raises the wiper arms 53 and 54 slightly at their tips to cause these tips to clear the toothed combs of the bank level into which they will be subsequently inserted. One arm of the release magnet armature carries a projection 38 (Figs. 4 and 6). which normally drops into one of the retaining teeth of the 14 secondary carriage; when the magnet is energised this is lifted upwards and out of the tooth. It serves to prevent the damage to the bank which would occur if the wipers could be driven in when they were not held upwards.

The secondary relay i5 is now energised to initiate a self-interrupted secondary driving movement, the circuit operations of which will be understood from the ensuing circuit description. The release of the catch 83 which forms an extension of the armature of relay 15 from engagement with pin H2 on the secondary driving cam 49 causes this cam to rotate and engage with the driving roller, whereupon the rotation of the main and subsidiary cam will proceed on the lines described in connection with the main cam 48 and subsidiary cam 13 under control of the driving roller and its local drive-engaging spring 64 until such time as relay [5 is released for instance when the outlet testing wiper which connects up therewith encounters a free outlet in the selected group in response to the step-bystep movement of the secondary carriage, which in being advanced carries with it the primary carriage and the wiper arms secured thereto.

The secondary carriage driving action is the same as for the primary carriage, the only difference being that cam 49 is adapted to produce a rectangular movement of the driving pin 63 for each half revolution it performs. A further difierence, as previously mentioned, is that the rotation of the cam commences on operation of relay I5 and thereupon continues until such time as this relay releases and interposes its catch into the path of one or other of the rotating pins H2 or H3 according to which halfrevolution of the cam is involved in the step concerned when the outlet testing wiper which connects up with control relay [5 encounters a free outlet. Fig. 11 shows an enlarged perspective view of the secondary driving arrangements in which, for the sake of clarity. the main driving cam is assumed to have been removed and which shows the essential shape of the subsidiary driving cam 6| which is adapted to engage with is case hardened runner 62, while the roller 65 serves as a pivot for the driving strip 60 carrying the driving pin 63.

As described in connection with Fig. 6, the secondary carriage retaining pawl 33 (Figs. 4 and 6) is attached by a pivot to the selector chassis and, as in the case of the primary retaining pawl 43, carries a case hardened pin I22 at its free extremity which engages into teeth in the opposite side of the carriage to the driving teeth. The projection 39 on this pawl passes under the secondary carriage in order to cooperate with the secondary driving pawl, but instead of being integral with the pawl as in the primary case it pivots on the pin and has a restoring spring I23 as shown in Fig. 6.

The step shown on the pivoted projection 39 normally engages with a stop I24 (Fig. 4) attached to the chassis in such manner as to hold the pin I22 out of engagement with the holding teeth. When the secondary driving pin 63 engages with the first driving tooth to initiate a step of the secondary carriage the projection 39 is driven inwards away from the stop on the chassis and then as the driving pin moves forward in the direction of secondary motion, the free end of the projection moves about its pivot in the same direction so that when the driving pin backs out of the ratchet at completion of the step the projection in following in sympathy will override its stop and will so allow the retaining pin to drop into position to provide the positive lock feature described in connection with the primary movement.

Although not shown in the drawing, it will be understood that there is an extension piece on the long arm of the secondary carriage 50 which normally engages with an operating roller for the secondary off normal spring set 4| (Fig, 6 and also Fig. 7 where it is shown partly broken away) whereby the latter is pressed when the carriage is in normal position and is released as soon as the carriage moves off normal to initiate suitable circuit changes,

As regards the secondary drive interrupter springs these will form the outer combination of the lower build-up of the secondary control relay 15 (Fig. 4) and their operating pin I25 will be adjacent the head of the driving strip 60. Hence when the driving pin moves into engagement and commences the forward driving movement the springs are allowed to make or break according to their function and to remain so until the driving pin withdraws at the end of the stroke. These springs are not used as interrupter springs in their normal accepted circuit sense, but simply indicates when the carriage is in motion. The only use that has been made of these in the circuits shown is to prevent the release magnet deenergising while the wipers are moving.

When the secondary motion is terminated by the release of the secondary relay the release magnet is de-energised to lower the wiper tips into the contact sets opposite which they have been positioned to effect the necessary connection between the incoming trunk and the selected outgoing trunk, while the stop 38 is again introduced into the retaining side of the secondary carriage ratchet.

From Fig. '7 it will be seen that the secondary retaining pawl 33 is in the form of a bell crank lever, the lower arm passing under the secondary off normal spring set 4| and engaging with a strip I26 attached to the release magnet armature, the end of strip I26 hooking behind the lever end of the pawl 33. When the magnet is ole-energised the action of this strip is to withdraw the pawl and its pivoted head projection away from the secondary carriage so that the step on the projection will once again re-engage with the stop l24 (Fig. 4) on the chassis so that the retaining pin will be out of action with the secondary ratchet when the release magnet is subsequently re-energised to initiate release of the switch,

When this occurs the removal of the projection 38 from the secondary carriage entirely frees this carrige which thereupon rapidl restores to its normal position under control of the helical secondary carriage restoring spring 8! and carrice with it the primary carriage.

The release of the latter has now to take place and this takes place as follows:

It will be seen from Figs. 4 and 4d that the primary retaining pawl 43 carries a spring-loaded pivoted piece 44 which is situated half-way down the pawl and this carries a similar step to the projection 39 on the secondary retaining pawl 33. In the normal position of the primary carriage the pivoted piece 44 engages with a small P jecting arm 45 secured at right angles to and at the centre of. the primary carriage by virtue of the contact between said arm and a pin secured in the pivoted piece 44. On the first primary step the arm will leave the pin but the piece 44 will not move since it will engage with the stop 42 afiixed to the release magnet assembly in the manner shown in Fig. 7. Each time the retaining pawl 43 is moved about its pivot away from th retaining teeth of the primary carriage during the primary step-by-step movement, the outward movement performed by the piece 44 which moves in sympathy with the pawl 43 will be insuflicient to cause the step thereon to engage behind the stop 42 so that during the primary stepping no locking action can be effected on the retaining pawl. When, however, the secondar carriage 50 makes a step and carries with it the primary carriage 52 and also the primary retaining pawl 43 which is pivoted on the secondary carriage, the movement involved by the first step will be sufiicient to allow the step on the pivoted piece 44 to drop behind the stop 42.

Hence, after the secondary release has taken place as described above, the step comes into action as shown in Fig. 4b and disengages the primary retaining pawl pin I I8 from the primary carriage so that this carriage will restore to normal under the tension of the associated helical restoring spring 80. The pivot piece 44 will then be disengaged by the projecting arm 45 on the primary carriage and which in the normal position of the carriage will engage with the pin secured in the piece 44.

On being disengaged from behind the stop 42 the pivoted piece allows the primary retaining pawl 43 to re-engage its pin in the primary toothed plate and the switch is mechanically ready for a subsequent setting operation,

Two further types of release are available for use on special circuits, one in which primary release takes place without any secondary movement, and the other, secondary release without involving restoration of the primary carriage.

For this function the stop 42 on the release magnet assembly is secured thereto by a pivot as shown in Fig, 7 and on the energisation of the release magnet the strip I26 secured to the magnet armature on moving inwards away from the extension piece I21 secured to stop 42 will allow the stop to rotate under pressure of a spring (not shown) about its pivot whereupon its top will move towards the primary carriage so as to give an effect equivalent to the movement of the secondary carriage off-normal. Hence when release after a primary movement only is required, the release magnet is energised as soon as the switch is moved off normal or at any time before the secondary movement has commenced. When the magnet is released stop 42 restores to its normal position and the primary pawl is therefore pulled out of engagement with the primary ratchet and the carriage thereupon restores.

For secondary release the same parts and adjustments are required. The release magnet circuit is completed through secondary off normal springs so that under ordinary conditions when the secondary carriage gets home the release magnet restores and pulls out the primary pawl so that the primary carriage now releases to restore the switch fully to normal. When secondary release only is required the release magnet is maintained via a subsidiary circuit so that on restoration of the secondary carriage the primary pawl is not pulled out and the selector can be further stepped in a primary direction and then in a secondary direction into another level.

Referring now to Fig. 10 which shows a sectional view of one form of main and subsidiary 20' mil steel. surface of the main cam .48 on the subsidiary spun over outside.

.17 cam assembly, say. that associated with the primary drive it willbeseen that the assembly comprises two pressings B8. and 59, each of, say, One,... 68,.which forms the outer cam 13 is on one side while. the other, 69. is a force fit inside the outer one .68 and takes the other side. The two halves are, also held together by the bronze bearing 61- which is dropped inside before the halves are pressedtogether and then Alternatively, the main and subsidiary cams might comprise a suitable mould ed plastic. The pins Illl, Ill, H2 and U3 of the cams might consist of a piece or pieces pushed up at right angles from the side, material of the cam or may comprise a pin or pins moulded in the cam if the unculded cam construction is adopted.

. It has already been mentionedthat instead of escapement control ,of a driving cam a simple catch construction could be utilised in conjunction with suitable circuit arrangements as previously described.

For instance, if a condenser was discharged into the controlling electromagnet, the electromagnet would only operate momentarily and restore to hold the drive until a fresh impulse is received. Bythis modification the primary and secondary camscan be identically controlled or alternatively if the controls. differ as described the secondary movement can be controlled both by dialled impulses and by hunting to find an idle line of a group.

For the purpose of indicating when the secondary carriage has completed its full travel the springset nearest the chassis on the secondary control relay [5 will be utilised and will be operated by a suitable projection on the secondary carriage when this carriage reaches the 11th step position.

As regards the selector wiring, it is thought that this might be effected with preformed cables. This can be.considered as starting at the plug 31 (Fig. 13) and entering the chassis through an ebonite hushed hole I33. Immediately inside the chassis one branch will extend direct to the primary drive, while the other branch continues to the release magnet and the springsets located within the chassis, and it will also extend out through another hushed hole to cater for the secondary drive.

From Fig. 13 it will be seen that the switch plug 3! engages with a jack II which is screwed to the vertical bank member l8. .'I 'he jack II is mounted on two separators giving sufiic=ent clearance between the jack and the vertical member to accommodate one arm of the selector chassis when it is slid into position. As regards the jacking-in and jacking-out of the selector, reference should be had to Figs. 4. '7, 11 and i3 and it should first be appreciated that the secondary drive including thecontrol relay [5 is assembled on. the U-shaped angle piece 89 (Fig. 11) and is readilydetachable irom the selector chassis, the control relay being electrically connected with the rest of the selector circuit via a branch of the. preformed selector wiring cable. With the selector in position against the bank as shown in Figs. 4 and 13 the plug 31 at the end of chmsis arm 3la engages jack 1| while an L-shaped shoulder piece on the same arm will engage a locating pin 128 (Fig. 13) in the bank upright ll. The other arm 3!!) of the chassis is of substantially L section and will at its slotted end engage with theextended bank clamp 18 rod .16 while the nut I29 (Fig. 4) will be tightened up to secure both the chassis arm 31b and also the bank (at this selector) to the supporting member I30 which connects with the relevant exchange mounting upright. Also engaging the clamp rod l6 at this point will be one slotted end of the angle piece 89 (not shown in Fig. 4), the other slotted end of which will engage a locating pin in the chassis arm (lib. Hence when it is desired to jack-out the selector it is first of all necessary to loosen off the locking nut I29 and then with one hand to hold the secondary unit in position while with the other hand the chassis is withdrawn. During withdrawal of the chassis the secondaryunit can be tilted inwardly so that it will clear the roller drive and it can then be withdrawn as well, this unit and the chassis being, as previously mentioned, linked by the wiring cable. When the selector. is to be jacked-in the opposite procedure is adopted so that the secondary unit is firstly manoeuvred into position and is followed by the coupled chassis after which the locking nut I28 is tightened up.

The carriage mechanism of the switch can be readily detached from the chassis for mantenance purposes. When rubbing wipers are employed this detachment may be obtained by employing a compact form or plug and socket in the circuit of the wiper cords.

A further point which should be noted is that although as, at present described the wiper tips perform two linear movements at right angles to one another followed by a slight movement of rotation when aselecting operation is being eifected, the invention also envisages the case where the last push-in movement is also l.near and at right angles to the first two main etting movements.

Turning now to the circuit arrangements, certain of the principles have been already laid down, and to these another will be added. The group and final selectors are to be kept as simple and standard aspossible, and all variations are to be made in the battery feed relay set which is jacked in as a separate unitand serves to control successive. switches. Apart from the question of standardisation one of the main advantages of this type of layout is the fact that any new technique can be introduced without affecting the mechanicalparts of. the exchange. One example of this as is described later is shown in the introduction of thespeed timing type of impulsing circuit (UnitedStates Patent No.2,334,5 91 granted November 16, .l943,. to, Taylor and Baker) by means of which impulse-responding circuits are adapted to function independently of the ratio of received impulses the, separate timemfiasuring functionsof. the ordinaryBand C relays bein combined into one timingfunctlon which simply measures the overall lengthof each impulse instead of th length of the separate parts thereof as hitherto.-...Withthenormal typeof exchange layout it would benecessary to modify every selector in the exchange. to. introduce this feature. Now it can be incorporated. or omitted merely .by

changing the first relay set, With the increased lengths of connectionover which dialling is being effected and thernore general use of A. C. methods, this point lsvery important.

Detailed circuit consideration of Figs. 2 and 3 will now be given and it will be understood that when the switch is to function as a group selector, 1. e.. with dialled primary movement and selfdriven secondary movement. and is to be controlled from a simple control circuit such as that of Fig. 3, then the primary driving cam will have to be of the two-stage escapement release type while the secondary driving cam will have to be of the single stage simple release type.

When a subscriber calls the control relay set or group of Fig. 3 is associated with the calling line via any suitable apparatus which might conveniently be of the line finder type. Relay A therein operates, whereupon the selector switch permanently associated with the control relay set is prepared for operation by the extension of earth forward over the negative and P leads. The earth on the negative lead operates the primary control relay VR, corresponding to relay 14 in the foregoing description, which at contacts orl prepares a locking circuit for itself on to the private P. The armature extension on relay VR allows the associated driving cam to rotate slightly to the second stop position and when relay A drops at the beginning of the first impulse relay VR releases in turn and frees the driving cam. Under local spring pressure it rotates further and engages with the roller and thereupon completes a revolution independently of the control relay VR as already described. On the next and subsequent impulses of the train the primary carriage is operated in a similar manner to cause it to advance a number of steps corresponding to the digit dialled and it will be noted from Fig. 3 that relays B and C are held operated throughout the train by virtue of their slugs, the B relay guarding the connection and maintaining the P lead earthed while the C relay maintains the Z lead open to prevent the premature operation of the release relay ZR. which is connected up to the Z lead on the first primary step due to the mechanical operation of the switch off normal contacts N I.

At the end of the first impulse train relay C releases after its slow release period and energises relay ZR which lifts the wipers clear of the bank level in question and at contact 2T2 provides an operating circuit for the secondary control relay RR. This relay in operating locks relay ZR at contacts rrl and also releases the catch on the secondary driving cam which engages with the roller. In this case the catch arrangement between the extension of the secondary relay armature and the driving cam is not of the escapement type, so that the motion continues until halted by the release of the relay RR and the consequent interposing of the tip of the extension armature into the path of the stop on the driving cam. The local drive-engaging spring periodically assists in maintaining the motion when the main cam passes throu h the position illustrated in Fig. 12. The secondary carriage advances step-by-step and carries with it the primary carriage and the wiper arms secured thereto are caused to enter step-by-step into the selected bank level. On the first secondary step the secondary oiT-normal contacts NRI and NR2 are mechanically operated so that the holding circuit of relay VR is transferred to the P lead at contact NR2 and is locked for the remainder of the call via resistance VRR.

At the end of each secondary step the operating circuit of relay RR is broken by the interrupter contacts TI which it will be understood are made during the engagement of the secondary driving pawl with the secondary ratchet, but when this occurs it will be noticed that the second winding of this relay will be connected over a rubbing test wiper P on to thecOrreSponding lead of an outgoing trunk. If such a lead is busy an earth potential will be encountered thereon so that relay RR will remain held and the secondary carriage will step on to the next set of outlets.

When a free set of outlets is encountered the P wiper will not encounter any earth potential and the interrupter contacts TI on opening will cause relay RR rapidly to deenergise and the catch on its armature will thereupon fall into position to halt the secondary movement when the cycle of movement of the cam is completed.

Relay ZR is now released and causes the wiper arms to drop so that the tips thereof will lower into the set oi. selected bank contacts to press the movable contacts against the fixed contacts in the contact bank and so causing the calling party and the battery feed relay set to be switched through to the succeeding selecting stage, which may be either the final selector stage or another group selector stage. If the latter the operation will be the same as previously described. If the former the operation of the battery feed relay set will be as described except that it will function twice while the circuits will be appropriately modified from those shown in Fig. 2. More detailed circuits are described in my Patent No. 2,402,232, above referred to.

If the calling party should now hang up, relays A and B in the control relay set will release and the removal of earth from the P lead will release relay VR, whereupon an operating circuit for relay ZR is re-completed via contacts m2 and NHL The wipers are again lifted clear of the bank and as previously described the primary and secondary carriages are now freed to restore to normal under local spring tension. The mechanically operated springs restore to normal and at contact NRI relay ZR is released to render the selector ready for further use.

As regards the succeeding selector, on seizure its primary control relay will have been operated over the negative lead and on release of relay A the control relay is released and initiates a single primary step. When relay B releases rela 0 releases following relay B and the selector release relay is energised and operates the secondary control relay whereupon a self-driven secondary movement commences. When a free outlet is encountered or when the 11th step position is reached where contacts equivalent to contacts SI (Fig. 2) are operated the secondary control relay releases to stop the drive and in turn releases the release relay. The release relay in restoring opens the holding circuit for the primary control relay which has been held during the secondary movement and the latter in restoring re-energises the release ma net whereupon the switch restores to normal in the same manner as has been described for the preceding selector.

If all outlets on a level should prove to be busy the wipers will advance to the 11th step position in which position the llth step contacts SI will be mechanically operated and will open the circuit of relay RR to halt the secondary motion in the same manner as for a free outlet so that the switch will contact the control relay set through to the 11th set of bank contacts. It will be understood that the llth step positive contact is permanently earthed so that earth will be extended back over the positive lead to the control group which in response thereto will initiate the return of a busy tone to the calling party in a manner discussed in the previously mentioned application. If an overflow for the level is to be provided this could be connected to the 11th step P contacts and the contacts SI in operating could be in the form of a changeover combination fim s22 adaptedto extend eartnrorward over tired-dishing s wentrwrmizvwonldebe returned toathermanuiac- Pwiper-toepenate theoverflow meter-i'ri thisconturer 'for rapairsorreeadjustment wheretherbest dition. possible'an'angements: for adjustment and/or re- 'The advantages of=the new invention arenset n palmwouldbe-available;"This feature would have out below I The ratchet and-pawl hammer driveofe fir -partioulan-cappeal iinrthe case ofprivate auto- Kath m Step b'y-Step' e t r :has b mativexobanges iwhere: skilled maintenance'perplaced by a very'smooth drive Not' onIwhave all sonnei aznd duttablemaintenancc equipment.:are tho-violent accelerations and-sudden stops' been tmot ordinarily.:available.' The sealed COVBRJGT- removed but also=the sharp edgdrivingnpawls, rrangements wouldzfurthermore provide an-efiecmjamming' operation and the like Thepenformiiflm'tivaremedy againstunnecessary wear and trouvanceof this selector should inthem'atter of 'ewear -ble wul'lichresu1ts-t rom..the ingress of dust and he immeasurablysuperior to its predecessors. abra'sives whichis :always likely to occur when This point would begreatlyassisted bvtthesine maintenancei ahdteduipment isuperformedzmn efcreasedibank tolerances; the primary-movement s sitesas is usuals'at' present. r has been'doubledpthe secondary controiilmarginzgm lmlaim:

greatlytincreasedxHence a greaternmountoof 1. In anrreleoteical switch. a movahle rcontact oivmationsnan bealiowed beforethingsebegimto v makingnmember, acrotating drivenza-ndtransfer emu- Thedireotnessof the-mechanism'shouldcbe means' between said driver and said member-joi- --.:nted. All mechanical springs areoperatedawithrenaming-Said? driver: to move said member step *by out the use of levers. Thisitact ragainqincreasem step in each of two directions in a plane perin the possible tolerances. .Ampiepower is available i pendicularito the axis of: rotation: of said driver,

and it; is no longer necessary. totworlrsascneamto the'i-eby to' bning said member into contact-mak- ;-;predetermined:limits as: hitherto. izrorder ta get a ingqaosition. ..-desire d performance. 2. An electrical switch'as claimed in claim. 1,

With regard to talking efiiciency :which is fiihgggs wherein 'said transfer means moves said member :2 thing the. subscriber is essentiallyrinteresteddn, step by stepmndefl the control OfSDaCBdIEPaI't r-alli-bankcontacts. are: made of silver instead; of l el'ectmeal impulses, and: wherein said transfer whilst metals-f pl p sures andcdual contacts means -causesasaid member to execute each step a. are provided. These contacts moreoveriareselfin a shonter period of time than the interval .be aligning :amdcannot shiftnwith. regard-to =eaclag (y tweensu'ccessive onesiof said impulses. other and'socause microphonicnoisesd Thepir- 32 -In an' electrical switch, a movable electrical cults also :have been- Sodesigned as to--roduce.the eontact rfiaking member, a rotatin drivel, 17111115- r-contactszin the speech. path to aminimum. In -fer'means betweensaid driverv and said member .1. a normal 10,000 lineexchange there are iabouts24 401-cailsingksaidrdflvl" to move said member step contact. points in the. talking circuit. neglectingr, 3 by step: in each oi' two directions in a plane "per- ...the pneselector or finder stage. In the proposed pehdiculanto the :axisof rotation of said driver,

system this number is reduced to 10. said transfer meansincluding a clutch mecha- Two other points of importance are spacessavrosin-for oorn'm'unicstingv the motion of said driver 7: ing and .battery drain. In the space of a IOGA" to 'saidi me'mber. during movement of the latter rack. where. normally 90 10110: selectors-ares 40*irr one ofisaid'directions and another clutch mechl. mounted, 300.0f the proposed selectors :cansbe anism .for communicating the mOtiO 'OfSBJd fitted. In a 10,000.lineexchangeease-considered, :drive'r=to:said:.member during movement of-the 38 racks were required to mountthegroup and latter in the other'of said directions.

.final selectors. With the selectors described here- 42: In amelectricalcswitch, a movable electrical in only the space occupied by 19.racks is required? 45eoomtactumakingu member; a rotating driver; Even under the mostadversecases considered the .txtransferzmeanss between said driver and said Percentage, Sp ce. Sav g was .very .h-ightanda in member: for :zcausing said driver to" move said many'cases exceeded member stepwby step breach of two directions in "From a manufacturing .pointotviewthe sea aplane'iperpendicuiar to the axis of rotation of .lector has much to recommend it. .Amongst otherihsaidwdriver; .said transfer means including 8. things are the greater tolerancesnmentioned 'E:clutch.mechanism for-communicating the motion earlier, the fewness and simplicity, of .parts.,in- Trot saidi-drivertosaid member during movement volved. The selector can be divided into. several n of the iatterinone of said directions, another "sub-assemblies for construction flexibility and a anclutchumechanismfor communicating the' molarge number of the parts are already standard-s. ttion-of said driver to'said member during move- 156d rsment oft-he latter ln'the other of said direction ro an ex a e ance point otview a sand means whereby at least one of said clutch furtherirnprovement might be incorporatedin umechanisms temporarily ceases to communicate the switch construction which would further enwthewmotionoflsaid driver to said member near hance itsvalue. Briefly, the switch cover c0uld.,60 the-end of each step taken by said member under -form an integral part of the switch and within the control of that clutch mechanism. which a short individual roller drive would be lo- 5. In. an electrical switch, a movable contact cated. To this drive would be coupled a pinion making member, a rotating driver, and transfer which would slightly project from the switch in means between said driver and said member for such manner as to engage with a corresponding-05 causing said driver to move said member step by pinion on a common motor driven driving shaft .step in-.each of two directions parallel to a par- 'when the switch is jacked into position. .The ticular. plane, and means for then moving said short roller drive within each switch would thus ..member in a direction substantially perpendicube in continuous rotation so long as the switch lar to said plane. is jacked in position and would be coupled up by, 6. In. an electrical switch, a movable contact the friction driving cams in the same manner. as making member occupying a particular position, coupling s effected with the common driving and'mechanism for imparting to said member roller. The advantage obtained is that each our successive movements thereby to bring said switch could be a sealed unit which would be sold member into contact making position, each said to a customer as such, and which, if anything-.75. movementbeginningwhere the immediately pre- 23 ceding movement ended and taking place along a path transverse to such preceding movement.

7. In an electrical switch, a movable contact making member having a normal position, mechanism for moving said member from said normal position in a particular direction to a second position, then moving said member from said second position in a direction substantially perpendicular to said first direction to a third position, and then moving said member from said third position in a direction substantially perpendicular to each of said first two directions, thereby to bring said member into contact making position, said mechanism including a rotating driver operative to supply the power for moving said member in two of said directions.

8. An electrical switch as claimed in claim 7, wherein the movement of said member each of two of said directions comprises a step by step movement.

9. An electrical switch as claimed in claim 7, wherein the movement of said member in at least one of said first two directions is a movement for a variable distance.

10. In an electrical switch, a movable contact making member having a normal position, continuously operating source of mechanical power, transfer mechanism for causing said source to move said member from said normal position for a variable distance in a particular direction to a second position, other transfer mechanism for then causing said source to move said member from said second position for a variable distance in a direction substantially perpendicular to said first direction to a third position, and means then operated to move said member from said third position in a direction substantially perpendicular to each of said first two directions, thereby to bring said member into contact making position.

11. In an electrical switch, a movable contact making member occupying a particular position, mechanism for moving said member from said position in a particular direction to a second position, then moving said member from said second position in a direction substantially perpendicular to said first direction to a third position, then moving said member from said third position in a direction substantially perpendicular to each of said first two directions to a fourth position, and then moving said member from said fourth position in a direction substantially perpendicular said third direction, thereby to bring said member into contact making position.

12. In an automatic switch for completing an electrical circuit over any contact in a coordinate field of contacts, a movable carriage, a continuously operating source of mechanical power, transfer mechanism for causing said source to move said carriage first longitudinally and then laterally in a particular plane to select any contact in said field, a member carried by said carriage, and means operated after a contact has been selected for moving said member in a direction transverse to said plane to complete an electrical circuit over the selected contact.

13. In an automatic switch for completing an electrical circuit over any contact in a coordinate field of contacts. a movable carriage, mechanism for moving said carriage first longitudinally and then laterally in a particular plane to select any contact in said field, a member carried over a series of contacts in said field by said carriage during said lateral movement, means operated before said lateral movement to move said member a certain distance in a direction transverse to said plane whereby, during said lateral movement, said member clears the contacts over which it is moved, said last means operated after said lateral movement to move said member in the opposite direction transverse to said plane thereby to complete an electrical circuit over the selected contact. i

14. In an electrical switch, a horizontal rectangular frame, two electromagnets carried -by said frame respectively along two non-parallel sides of said frame, a contact making member movably supported upon said frame, a rotating driver, transfer means controlled by one of said electromagnets for causing said driver to move said member step by step in one direction, and

other transfer means controlled by the other of said electromagnets for causing said driver to move said member step by step in a difierent direction, thereby to bring said member into contact making position.

15. In an electrical switch, a plurality of groups of contacts, each contact including a movable conductor and a stationary conductor, a plunger having a normal position, mechanism for moving said plunger in one direction to select a group of contacts and then moving it in a different direction to select a particular contact in the selected group, and means for finally moving said plunger in a third direction to engage the movable conductor of the selected contact and move it into electrical connection with the stationary conductor of the selected contact.

16. An electrical switch as claimed in claim 15, wherein said mechanism derives its power from a rotating member, and wherein each of said first two movements of said plunger is in a plane perpendicular to the axis of rotation of said member.

17. An electrical switch as claimed in claim 15, wherein said mechanism derives its power from a rotating member, wherein each of said first two movements of said plunger is in a plane perpendicular to the axis of rotation of said member, and wherein said final movement is substantially parallel to said axis.

18. In an electrical switch, a plurality of groups of contacts, each contact including a movable conductor and a stationary conductor, a plunger having a normal position, mechanism for moving said plunger step by step in one direction to select a group of contacts and then moving it step by step in a different direction to select a particular contact in the selected group, and means for finally moving said plunger in a third direction to engage the movable conductor of the selected contact and move it into electrical connection with the stationary conductor of the selected contact.

19. In an electrical switch, a plurality of groups of contacts, each contact including a movable conductor and a stationary conductor, a plunger having a normal position, mechanism for moving said plunger step by step in one direction to select a group of contacts and then moving it step by step in a diilerent direction to select a particular contact in the selected group, said mechanism including means for causing said plunger to execute each step with constant acceleration and deceleration, and means for finally moving said plunger in a third direction to cause the movable conductor of the selected contact to move into electrical connection with the stationary conductor of the selected contact.

20. In a switching system, a plurality of paralle elongated stationary conductors, a plurality o 25 groups oftmovable contactors, eachgroup include, ing a different contactor for eachstationarysconvductor, means supporting. the differentgroupspf contactors at regularly spaced intervals alopg the length of saidstationary conductors, so;,that-, j each contactor is adjacent its individual station; ary conductor, differentmechanisms corresponding respectively to the different groupstoflcon tactors, and means for operatingreach mecha-,-,

nism atltimes first to selectany contactorin its l associated group and-then to move the [select-ed, contactor into engagement withits individualsta a, tionary conductor.

21. A switching system as claimed-inclaim wherein each of said groups of contactors is die 5.

vided into a pluralityof subfloupaandwherei said selective operation of any mechanlsmioom- -t prises a movement in one direction to select ve, particular subgroup in the group oftcontactcss associated with that mechanism and a subs quent movement in a different direction 'to-seleq a particular contactor in the selected subgroup 22., A switching system as claimed in claim 20; wherein all of said mechanisms are operated-by 5 power derived from a common rotating r-shaft g which is parallel to said elongated :conductors 23. In a switching system-as c1aimed.in elaimg 20,v a support for said conductors and said -contactors, and means including a jack for detach ably securing each of said mechanisms to said go support.

24 .;In a switching system, a plurality of groups vv of elongated primary conductors, all of saideo n ductors being parallel and each: group thereof saidd ivme, m mb r. ai o camsr epcret nsip i part vm i said t n fe member d r: s eirq or said d iving m m er-e cvcl i e ement, a d; eans .s ntroll d 1 by d t ans e emb r 14991. ,s ch. c c movement: for. iv s ids eiac malringdeyice .stepby stepw 27, .A d iving m ch n m. s "c aimed i c im 26, wherein, said w c ms comnri e..,a si e 1 11. tary rotatablememben,

23, ,In an electrical switch, ,a movable ,C ILaQlZW maklng device, a transfermember having a pair ofcarns rotatably supportedthereon, a fixedsur; face, a moving surface, means for movably supporting said transfer member .so that one. of said camslengages ,saidrfixerd surfa e, a d t e o her, of said cams engages said movingsuri'ace said moving. surface effective to rotate said .othercam means whereby the rotation of saidtotherrcam is communicated to saidone cam,,.sa,i,d,two,ror-,,,- tating cams cooperating to impartto said transfer emher a cy c movement, e ns ntrol ed:

bythe cyclic movement of said transfer-member for driving said contact, making device step, by WIM 29; In an electrical switch, a toothed member to bedriyen, a continuously operatingdriven a, fixed surface, a transfer membenhaving a pa1r,. f cams. r tat b v pport d t ereona nat slidably and rotatably mounting said, transfer b r at. one, of said cams engageslsald 'surface and the othertofsflid c m r saees eu driving member, sa d two cams cooperatingt'o 1m 1 part to said transfer membena movement such that a certain, portion ,thereofntravels in ,a sun- Occupyingv a plane parallel to thefplanesrgcwplgdj stantially rectangular, path. said portion efiective by the other groups, a plurality of groupsef sec-. ondary conductors, each of said SECOIidfiIY'COII-g ductors-being transverse to the length -of said.-. primary conductors and each group-ofsecondary,--

to move said toothed member step bystenbyentering each tooth inturn, moving lsaidmember, one step, leaving that tooth andreturning to a point adjacent the nexttooth, and a contact :mak

conductors being substantially in a plane parallel 40 ing member conne-ctedv to Said topthedd' u and adjacent to the plane occupied by a pax ticular group of primary conductors, each secondary conductor having different integral portionsoor responding respectively to different primary cone;

ductors in the adjacent group, and mechanismgfir operated first to select any one of said'portions and then to move the selected portiorrintov on gagement with its corresponding primarycom ducton.

25. In a switching system, a plurality ofrgroups-ip of elongated primary conductors, all of saidooiaductors being parallel and each group thereof go 1. cupying a, plane parallel to the planes -ocoupied by the other groups, a plurality of groups M15603! ondary" conductors, each of said-secondary con 5 ductors being transverse to the length of said primary conductors and each group of secondary conductors being substantially in a plane .paral-q lel and adjacent to the plane occupied by a pa try. tlcular group of primary conductors, a, contact making member, mechanism for moving said member in one direction to select a particular secondary conductor and moving it in a different direction to select a particular primary conductor,- said-member effective after it has been moved in: both of said directions to complete an electricah circuit between the selected primary and second-; ary conductors.

26.-In an electrical switch, a movable contact making device, a continuously operative driving member, a fixed surface, a tranSfer-inember having a pair of cams rotatably supported thereon means for slidably and rotatably mountingsaid transfer member so that one of said cams engages said surface and the other of said cams engages 75 'and movedthereby stepby step..

30; In; a driving mechanism asclaimediniclaiin 29, a detent cooperating with said toothed mem her to prevent retrograde, ,movement v thereoi when said portion of the transfenmemberis not-, in a tooth andmeans controlled bythe-entr-y i of said transfer member into a tooth. forreleas v ing said detent.

31. In anelectricalswitch, a movable contactpialging .device, a transfer element ,carrying a w member rotatably mountedthereonr arotating drum; a, pair of spaced apart supports occupy ing fixed positions with respect to. the-axis of.- rotation of saiddrum; yieldable means tending 5 to.main tain one surface of said transferelement in engagement with oneof said,v supports, tend ing to maintain one surface of said rotatable mern her in engagement with the other of ,said-sup ports and tending to maintaina different surface of said rotatable'member in engagement with saidrotating drum;. said drum being efiective to rotate said member, and saidtsur'faces of said F member being so configuredas ,toimpart to said transfer element a. predeterminedmovement,with A p ct to sa d supports; and means controlled; by said transfer element upon such movement for i. driving saldcontact making device stepby .step. r 32, In an electrical switch, a movablecontact making ,device,, a transfer element carrying ea member rotatably mounted thereon; a rotating drumya pair of spaced apart supports occupy-HM ing, fixed positions with respect to theaxis of. rotation of, said drum; a singletspring ,applying such a force to said transfer element that it tends to maintain one surface of said transfer element 

